Internal fixation devices, such as plates, pins, rods, wires and screws, are often used to stabilize and join bones. For example, a bone plate can be used to facilitate healing of bone fractures or to fuse adjacent vertebral bodies of a patient's spinal column. The plate is placed against adjacent bone tissue and screws are inserted through screw holes of the plate into the adjacent bone tissue to anchor the plate into proper position.
Many bone plates are of fixed height or expandable. Fixed bone plates are manufactured in various heights so that one plate can be selected to best fit adjacent bone tissue. Alternatively, an expandable bone plate has an adjustable height to maintain spacing of the vertebrae above and below the removed vertebral or disc material. Both types of bone plates have limitations and problems. Fixed bone plates have good structural integrity but can be cumbersome to place. Further, the fixed bone plate must be exactly the correct height. If the bone plate is too large, it can cause over distraction to the vertebral bodies or damage the vertebral body above and below the bone plate. If the bone plate is too small, it can displace out of position. Expandable bone plates are much easier to correctly size and place. However, the mechanical mechanism used to expand the bone plate may fail after implantation. The interconnection between components of an expandable bone plate should be secure enough such that the bone plate does not disassemble prior to or after implantation.